Simplified methods of measuring kidney function are needed in order to facilitate monitoring of kidney disease progression and to assess the impact of disease modifying therapy in the clinic. Use of methods which require urine collection are often tedious and difficult for the patient to execute. Therefore, the objective of this study is to validate a single- injection plasma clearance method of para-aminohippurate (PAH) and iothalmate to measure effective renal plasma flow (ERPF) and glomerular filtration rate (GFR), respectively. Sixty volunteers with various degrees of renal insufficiency will be evaluated. Renal function will be evaluated following a single injection of PAH and iothalamate. The results will be compared using statistical analysis to determine the precision, bias and correlation of the plasma and renal clearance methods.